The invention relates to hydraulic valve lifters and more specifically to variable duration valve lifters.
Variable duration hydraulic valve lifters are an improvement upon the basic hydraulic valve lifter which has applications in high-performance engines. The radical cam of high-performance engines causes valve overlap which is effective in improving engine performance at high speeds, but causes very rough engine performance at idling. The variable duration, or "bleed down", lifter solves this problem. U.S. Pat. Nos. 3,921,609, 4,524,731, and 4,913,106 are directed to prior art variable duration hydraulic valve lifters. Thorough descriptions of the purpose and functioning of bleed down hydraulic lifters are found in these patents.
When an engine is cammed for more power, its ability to breath is effectively increased by opening the valves wider and holding them open longer. Keeping them open longer is known as increasing the duration of the cam. Theoretically, the exhaust valve of each cylinder opens when the piston reaches bottom dead center of the power stroke and remains open as the piston rises to top dead center on the exhaust stroke. At this point the intake valve opens and the exhaust valve closes. This is generally speaking how the valves are timed on a stock engine.
In order to extend the total duration of the valves, the exhaust valve must open before the piston reaches bottom dead center and close after the piston reaches top dead center, and the intake valve opens before the piston reaches top dead center and closes after reaching bottom dead center. This gets into a situation known as overlap: the intake valve opens before the exhaust valve is fully closed producing a period when both valves are open simultaneously.
At high rpm, despite the overlap, the increase in the ability of the engine to breath increases engine power. However, at low rpm, just the opposite is true, and the more radically varied the cam is, the greater is the overlap period, and the greater the power loss at low rpm. A car modified with a radical cam is hard to start, idles very roughly, and lacks low speed power.
At low and mid-range rpm (3500 rpm or less) the overlapping of the exhaust and intake valves being open at the same time result in a loss of horsepower and torque, result in incomplete combustion causing increased emissions and a decrease in gas mileage.
Stock factory engines are set up to primarily use engine oils such as 5 wt, 10 wt, 20 wt, and 30 wt. They are designed to use multi-weight oils such as 10-30 wt, 10-40 wt, 15-40 wt, etc. Existing variable duration valve lifters having straight external grooves in the external surface of their plungers, such as described and illustrated in the Rhoads patents, cannot function efficiently with multigrade engine oils. The oil passes along these grooves in spurts and not with a controlled steady flow. The recovery time for the oil to leave the reservoir areas of the variable duration valve lifters, pass along their respective external grooves and return to their respective reservoir areas is excessive making their operation inefficient.
It is an object of the invention to provide a novel variable duration hydraulic valve lifter that will reduce emissions by accomplishing complete combustion of the gases burned in the engine.
It is also an object of the invention to provide a novel variable duration hydraulic valve lifter that will increase an engines horsepower and torque.
It is another object of the invention to provide a novel variable duration hydraulic valve lifter that will increase gas mileage.
It is a further object of the invention to provide a novel variable duration hydraulic valve lifter that can be used effectively with multiweight engine oils and which can provide a controlled steady bleed flow along its respective external grooves in its plunger.
It is an additional object of the invention to provide a novel variable duration hydraulic valve lifter that can drastically reduce the recovery time for oil to leave the reservoir areas and pass along their respective external grooves of the plunger and return to their respective reservoir areas.